Loose grounds can cause all sorts of fun; on the 85 300D I had the following symptoms: RH blinker would not work with lights on and in reverse -or- with lights on and foot on brake
RH Front blinker and dash blinker was illuminating very dimly under those conditions, and somewhat noticably when all three occurred. I ultimately traced it to the ground wire on the RH Rear bulb cluster; the bolt holding it had someply come loose. Snugging the bolt back up made the problems all go away! I hope you get that lucky! -j.
